Extraction of aromatic hydrocarbons from mixed hydrocarbons with a silver salt and an alkane sulfonic acid



OC- 30, 1956 c. E. JOHNSON l-:T Ax. 2,768,986

DXTRACTIDN oF -ARDMATIC HYDROCARBDNS FROM MIXED HYDRocARBoNs WITH A SILVER SALT AND AN ALKANE SULFONIC ACID Filed Nov. 26, 1952 United States Patent O EXTRACTION F AROMATIC HYDROCARBONS FROM MIXED HYDROCARBONS Wi'IH A SIL- VER SALT AND AN ALKANE SULFONIC ACID Carl E. Johnson, Griffith, and Arthur P. Lien, Highland, Ind., and David A. McCaulay, Chicago, lil., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application November 262, 1952, Serial No. 322,754

7 Claims. (Cl. 26.0-6174) This invention relates to the separation of aromatic hydrocarbons from a mixture of hydrocarbons. More particularly it relates to the recovery of aromatic hydrocarbons from an olenic hydrocarbon-free and organic sulfur compound-free petroleum naphtha.

There is a considerable demand for aromatic hydrocarbons, particularly the lower boiling monocyclic aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene. Petroleum fractions are a good source of these aromatic hydrocarbons, particularly those fractions cbtained by the catalytic treatment of virgin naphthas, e. g., from the so-called hydroforming process and platforming process.

An object of the invention is the separation of aromatic hydrocarbons 'from a mixture of hydrocarbons; preferably from a mixture of hydrocarbons that is essentially free of oleinic hydrocarbons and organic sulfur compounds. Another object is the recovery of aromatic hydrocarbons from petroleum distillates, preferably distillates boiling in the gasoline range, i. e., below about 400 F. (200 C). Yet another object is the recovery of essentially pure aromatic hydrocarbons from a mixture of hydrocarbons. A particular object is the recovery of aromatic hydrocarbons from a mixture of hydrocarbons by treatment of said mixture with an alkanesulfonic acid and a silver sa-lt soluble in the acid. A further object of lthe invention is the recovery of aromatic hydrocarbons from a solution consisting of said aromatic hydrocarbon and alkanesulfonic acid and a soluble silver salt by displacement therefrom with an added monocyclic aromatic hydrocarbon having a boiling point of not more than about 180 C. A preferred object is the recovery of benzene, toluene and Cs aromatic hydrocarbons from a hydroformate or platformate which is essentially free of olenic hydrocarbons and organic sulfur compounds.

The above objects and other objects not set out separately are attained by contacting a hydrocarbon mixture n molecular Weight aromatic hydrocarbon, e. g., trimethylbenzene can be displaced by contacting the extract phase with xylene, toluene or benzene. Thus in the case of an extract phase containing aromatic hydrocarbons with a molecular weight higher (or loosely speaking, higher boiling) than benzene, these aromatic hydrocarbons can Vbe displaced from the extract phase by contacting the extract phase with a sufcient amount of added benzene.

The alkanesulfonic acid of this invention may be any alkauesulfonic acid which can exist as a liquid at a temperature 'below the decomposition 'temperature `of the ICC acid. Thus acids having from one to as many as nine or more carbon atoms can be used. For ease in operation it is desirable to operate with alkanesulfonic acids Which are liquids at ambient temperatures and which have relatively high decomposition temperatures. The preferred acids are those which have the sulfonic group attached to the end carbon atom of a straight hydrocarbon chain. Eecause of their melting points and relatively high decomposition points and relatively highboiling points, the preferred alkanesulfonic acids are methanesulfonic acid, ethanesulfonic acid and lpropanesulfonic acid.

As an example of the thermal stability of the preferred acids, ethanesulfonic acid is unaffected by heating for 4 hours at C. and only 1% is decomposed by heating for 4 hours at 180 C. Methaneethaneand l-propaneare the most stable alkanesulfonic acids, in that order.

The boiling points and melting points of the preferred alkanesulfonic acids are given below:

The process of this invention is carried out under liquid phase conditions. Therefore, it is necessary that both the mixed hydrocarbon feed and the alkanesulfonic acid be liquids. Thus the temperature in the contacting zone must be at least high enough to maintain the particular alkanesulfonic acid in the liquid phase. Elevated temperatures can be employed by the use of sufficient pressure to maintain the hydrocarbons in the liquid phase. The maximum temperature 0f operation must be below the temperature at which appreciable decomposition of the alkanesulfonic acid occurs. The desirable maximum temperature of contacting is about C. Elevated temperatures have an appreciably unfavorable effect on the selectivity of aroma-tic separation so that temperatures below about 50 C. are desirable. It is preferred to operate at temperatures between about 0 and 30 C. It is to be understood that, even at the preferred range of temperature, the temperature of operation must be high enough to maintain the alkanesulfonic acid in the liquid state.

The presence of water in the alkanesulfonic acid has an adverse effect on the selectivity of the treating agent. Amounts of Water up to about 5 weight percent can be present. It is preferred to operate with alkanesulfonic acid that is essentially anhydrous, i. e., the acid should contain less than about l-2% of water. ln order to keep the water content of the acid low, it is preferred to operate with essentially anhydrous feed.

Commercial purity alkanesulfonic acid contains about l-2% of sulfuric acid. Under the preferred operating conditions of the process the sulfuric acid sulfonates some of the aromatic hydrocarbon in the extract phase. The presence of arylsulfonic acid in the contacting zone is detrimental because of the formation of solid hydrates. It is preferred to operate with alkanesulfonic acid that is essentially sulfuric-acid free.

The amount of alkanesulfonic acid used in the contacting zone must be at least suflicient to form separate rai'linate and extract phases, i. e., the amount of acid present must exceed the solubility of the acid in the mixed hydrocarbon feed. More than this minimum amount should be used, e. g., about l0 volume percent, based on mixed hydrocarbon feed. Quite large amounts of acid may be used, as much as 300 volume percent or more; operation With excessively large amounts results in a reduction in the purity of the aromatic hydrocarbons in the extract. It is preferred to operate with amounts of alkanesulfonic acid, based on mixed hydrocarbon feed, of between about 50 and 120 volume percent.

It has been discovered that the presence of certain ilver salts in alkanesulfonic acid greatly increases the ability of the alkanesulfonic acid to dissolve selectively aromatic hydrocarbons. This increase in solubility is particularly great in the lower molecular weight alkanesulfonic acids, i. e., methanesulfonic acid, ethanesulfonic acid and l-propanesulfonic acid. The silver salts that are useful for this purpose must have a very high solubility in the particular alkanesulfonic acid. The silver salts of this invention are silver sulfate and silver alkanesulfonate. Preferably, the silver alkanesulfonate should be the salt of the particular alkanesulfonic acid being used in the process, e. g., when using ethanesulfonic acid the silver salt should be silver ethanesulfonic acid. However, it is to be understood that this is not an essential requirement of the process and different salts may be used or mixtures of salts may be used with a particular alkanesulfonic acid or with mixtures of dierent al'xanesulfonic acids. Furthermore, mixtures of silver sulfate and silver a kanesulfonate may be used. lt is preferred to operate with at least one member selected from the group consisting ot' silver sulfate, silver methanesulfonate, silver ethanesulfonate and silver l-propanesulfonate.

The amount of silver salt present in the treating agent, which treating agent consists essentially of alkanesulfonic acid and the silver salt, may be as little as a trace. The solubility of the silver salt in the alkanesulfonic acid is increased by the presence of aromatic hydrocarbons therein. This is believed to be caused by the interaction of acid, aromatic hydrocarbon and silver salt to form an adduct or complex, which complex is extremely soluble in the acid. However, an upper limit exists on the ability of the acid to dissolve silver salt even in the presence of aromatic hydrocarbon; the presence of silver salt in excess of lthe amount that can be dissolved in the extract phase does not further improve the ability of the acid to dissolve aromatic hydrocarbons. The upper limit on silver salt usage is the limit of solubility in the extract phase, i. e., the amount of silver salt added to the contacting Zone should be such that no separate phase of solid silver salt is present therein. Normally less than this maximum amount of acid will be used. In general it is preferred to operate with l gram atom of silver (as silver salt) in the contacting zone per mol of aromatic hydrocarbon in the mixed hydrocarbon feed. The preferred treating agent consists of defined alkane sulfonic acid and defined silver salt, said silver salt being present in an amount that exceeds the physical solubility of said silver salt in said alkane sulfonic acid, i. e., the agent consists of alkane sulfonic acid, physically dissolved siiver salt and solid silver salt particles dispersed in said alkane sulfonic acid; this treating agent appears to be a liquid and may be considered as such in operation of a unit.

The feed to the process may be any mixture of hydrocarbons which contains appreciable amounts of aromatic hydrocarbons, preferably monocyclic aromatic hydrocarbons. While any mixture of hydrocarbons can be utilized, it is preferred to operate with mixtures of hydrocarbons derived from petroleum. These may be naturally occurring mixtures derived by distillation from crude oil or they may be derived from the various processes that produce aromatic hydrocarbon-rich fractions, e. g., the hydroformate or platformate products produced by the catalytic treatment of straight run naphthas in the so-called hydroforrning and'platforming processes. Since the largest demand for aromatic hydrocarbons is for benzene, toluene and xylenes, it is preferred to operate on a hydroformate or platformate containing these aromatic hydrocarbons, i. e., fractions boiling between about 100 and 385 F.

Olenic hydrocarbons present in the feed react with the treating agent to form esters. These esters are thermally unstable; when the extract phase is heated to distill the aromatic hydrocarbons, the esters decompose and precipitate free-silver. Organic sulfur compounds present in the feed also react with the treating agent to form thermally unstable materials; these materials decompose on heating to precipitate free-silver. In order to avoid the loss of silver salt by these side reactions, it is preferred to operate on a mixed feed which is essentially free of olefinic hydrocarbons and organic sulfur compounds. Many methods of treating a raw feed to remove these undesired compounds are known to the art, e. g., treating with sulfuric acid or with liquid HF.

The extract phase obtained by the contacting of the mixed hydrocarbon feed with the treating agent consists of alkanesulfonic acid, silver salt, aromatic hydrocarbons and some non-aromatic hydrocarbons. The amount of non-aromatic hydrocarbon present will be dependent somewhat on the conditions of contacting, i. e., temperature, amount of silver salt, amount of acid, type of acid, type of feed, etc. It has been found that these non-aromatic hydrocarbons can be displaced from 4the extract phase by washing the extract phase with a hydrocarbon that is inert to the action of the treating agent and preferably is easily separable from the aromatic hydrocarbons by distillation. Examples of suitable inert hydrocarbons are butane, pentane and hexane. lnert hydrocarbons which boil higher than the aromatic hydrocarbons can be used when operating under conditions such that the higher boiling inert hydrocarbons can be recovered from the extract phase by distillation. The amount of inert hydrocarbon used for washing purposes will vary somewhat with the amount of non-aromatic hydrocarbon present in the extract phase. The amount of wash hydrocarbon used should be held to a minimum as the wash hydrocarbon does displace some of the aromatic hydrocarbons. By control of the conditions of Washing it is possible to displace the close boiling non-aromatic hydrocarbons with substantially no displacement of aromatic hydrocarbons.

The extract hydrocarbons present in the extract phase can be recovered in several ways: The simples procedure for experimental purposes involves the dilution of the extract phase with water. The addition of a suicient amount of water to the extract phase results in the formation of an upper extract hydrocarbon phase and a lowel aqueous phase which contains the alkanesulfonic acid and the silver salt. The extract hydrocarbons are separated by decantation and are freed of dissolved and occluded aqueous phase by treatment with aqueous caustic solution.

Another method of separating the extract hydrocarbons from the extract phase involves the neutralization of the alkanesulfonic acid, e. g., by treatment with ammonia or solid caustic; preferably the neutralization is carried out with an aqueous solution of the alkaline agent. The extract hydrocarbon layer can then be decanted from the lower layer of neutralized acid and silver salt.

The methods described above are suitable for use with any alkanesulfonic acid because they eliminate the problem of thermal decomposition of the acid.

When operating with mixed feed containing aromatic hydrocarbons which boil, either at normal pressure or under vacuum, at temperatures well below the decomposition temperature of the particular alkanesulfonic acid, the aromatic hydrocarbon can be readily separated from the extract phase by distillation therefrom. The recovered treating agent consists of the alkanesulfonic acid, dissolved silver salt and solid salt. The solid salt exists as extremely iine particles dispersed in the acid. The dispersion is quite stable and does not precipitate solid salt even on standing for several hours. The dispersion of solid silver salt in acid is readily pumpable. In the process design of a unit, the dispersion can be considered to be a liquid.

Thus benzene can be distilled away from an extract phase consisting of benzene, methanesulfonic acid (or ethanesulfonic acid or l-propanesulfonic acid) and silver sulfate (or the corresponding silver alkanesulfonate) by heating the extract phase to 150 C., preferably below about 120 C. Trimethylbenzene can be recovered from an extract phase by operating at about 150 C. at about 10 mm. Hg pressure. In order to recover substantially all the aromatic hydrocarbon from the extract phase, it is necessary to operate at a temperature considerably higher than the boiling point of the aromatic hydrocarbon or conversely, at a pressure considerably lower than that predicted from the vapor pressure curve of the aromatic hydrocarbon at the particular temperature of operation.

Still another method for separating the aromatic hydrocarbons from the extract phase has been found. This method is particularly suitable when the aromatic hydrocarbons boil at a temperature such that distillation cannot be used without appreciable decomposition of the alkanesulfonic acid. It is preferred to use this method when the boiling point of an aromatic hydrocarbon at normal pressure exceeds about 180 C., e. g., monocyclic aromatics containing 10 or more carbon atoms. When operating with the preferred alkanesulfonic acids no appreciable decomposition will occur when distilling, under vacuum, the extract phase at a temperature corresponding to 180 C. at normal pressure, i` e., 760 mm. Hg; however, to minimize the risks inherent in operating so near'the appreciable decomposition temperatures, it is preferred to use the displacement technique with all alkanesulfonic acids when one of the aromatic hydrocarbons in the extract phase boils above about 180 C. at normal pressure.

It has been found that an aromatic hydrocarbon can be displaced from the extract phase by contacting the extract phase with an added lower molecular weight aromatic hydrocarbon. To illustrate, trimethylbenzene can be displaced by xylene, and toluene can be displaced by benzene. It is preferred to use as the displacing aromatic hydrocarbon a monocyclic aromatic hydrocarbon which has a boiling point of not more than about 180 C. at normal pressure and preferably boils below or at the same boiling point as the lowest boiling aromatic hydrocarbon present in the extract phase. For

example, in the case of an extract phase containing benzene and higher boiling aromatic hydrocarbons, the displacing hydrocarbon should be benzene. In the case of an extract phase containing toluene and higher boiling aromatic hydrocarbons, the displacing hydrocarbon should be either toluene or benzene.

The amount of displacing hydrocarbon is dependent somewhat on the type of hydrocarbon being displaced and also upon the eiciency of the contacting operation. When operating with an eflicient countercurrent contacting zone at a temperature between about and 30 C., an extract phase containing xylene as the sole aromatic hydrocarbon should be contacted with between about and 7 mols of benzene per mol of xylene in order to Vdisplace about 95% of the xylene. By using a suicient number of extract stages in the countercurrent contacting, as much as 99% of the xylene can be displaced using this amount of benzene. In order to obtain a 95% displacement of xylene in the extract phase, it is necessary to use between about 10 and 15 mols of benzene per mol of xylene when using a single batchwise contacting operation. The amount of displacing hydrocarbon needed in any particular case can be readily determined by experiment.

A preferred embodiment of the process of this invention is illustrated in the annexed figure which forms a part of this specification. The embodiment illustrated is schematic in nature and many items of process equipment have been omitted. These items may be readily added thereto by those skilled in the art.

Feed from source 11 is passed through line 12 into mixer 13. The feed in this illustration consists of the fraction boiling between about and 385 F. derived by the distillation of a hydroformate product. This fraction contains about 45 volume percent of benzene, toluene, ethylbenzene, xylene, C9 aromatic hydrocarbons and C10 aromatic hydrocarbons. In addition the feed contains about 1% of oletinic hydrocarbons and about 0.03 weight percent of sulfur; the remainder consists of parafnic and cycloparainic hydrocarbons.

lt is desired to remove the olenic hydrocarbons and the organic sulfur compounds from this feed prior to separating the aromatic hydrocarbons.

ln this illustration the olenic hydrocarbons and organic sulfur compounds are removed by treating the feed with sulfuric acid. From source 16, 98% sulfuric acid is passed through line 17 into mixer 13. Five pounds of H2804 are used per barrel (42 gal.) of feed. Mixer 13 is provided with heat exchange coil 18 which maintains the temperature of the contents of the mixer at about 20 C. The H2804 and the feed are thoroughly agitated in mixer 13 for a time long enough to remove the oleiinic hydrocarbons and organic sulfur compounds, but not long enough to sulfonate any of the aromatic hydrocarbons. A suitable contacting time is 5 minutes.

From mixer 13 a mixture of treated feed and acid sludge is passed through line 21 into settler 22. In settler 22 a lower layer of sludge is separated and withdrawn to sludge disposalby way of line 23. An upper layer of treated feed is withdrawn from settler 22 by way of line 24 and is passed into mixer 26.

Aqueous caustic, 10% NaOH, in an amount of about 50 volume percent based on treated feed is passed from source 27 through line 28 into mixer 26. The aqueous caustic and treated feed are thoroughly intermingled in mixer 26 for a time suiiicient to neutralize the acid ldissolved and occluded in the treated feed. The contents of mixer 26 are passed by way of line 31 into settler 32.

A lower aqueous layer of waste caustic is withdrawn from the settler 32 and is passed to waste disposal by way of line 33. -An upper neutral feed layer is withdrawn from settler 32 and is passed by way of line 34 into drier 36.

Drier 36 is a vessel lled with a medium for removing dissolved and occluded aqueous caustic from the neutral feed. Drier 36 may be iilled with steel Wool, rock salt, alumina balls, etc. Herein drier 36 is filled with alumina balls. Dried feed essentially free of water is withdrawn from drier 36 by way of line 37. Periodically drier 36 is revivified by methods well known in the art.

The essentially olenic hydrocarbon and organic sulfur compound-free feed in line 37 is passed through heat exchanger 39 and line 41 into extractor 42. Extractor 42, is a continuous countercurrent extraction tower which provides about ve theoretical extraction stages. .Extractor 42 may be filled with acid-resistant packing such as Raschig rings, Berl saddles, etc., or may be equipped with bubble trays or sieve plates. In this embodiment all the equipment exposed to alkanesulfonic acid is made of type 304 stainless steel.

Extractor 42 in this illustration is maintained at a temperature of 30 C. However, the extractor may be provided with heat exchangers so that a temperature gradation may be maintained over the height of the tower.

Methanesulfonic acid from source 46 is passed through line 47 into vessel 48. Silver methanesulfonate from source 51 is passed through line 52 into vessel 43. ln vessel 48 the silver salt is mixed with the acid and the temperature of the treating agent is adjusted to that desired in the extractor. Herein 70 volume percent of methanesulfonic acid is used based on feed from line 41; and 1 g. atom of silver is used per mol of aromatic hydrocarbon persent in the feed from line 41. The treating agent is passed from vessel 48 by way of line S4 into an upper point of extractor 42. Extractor 42 is operated with the interface slightly below the point of treating agent entry, i. e., high level operation.

Extractor 42 is operated so that about 10 minutes of contacting time is obtained in each extraction stage or a total residence time of about 1 hour. The rarIinate phase containingy dearomatized oil, dissolved treating agent and occluded treating agent is withdrawn from extractor 42 and passed by Way of line 56 into separator 57. In separator 57 occluded treating agent is removed from the raffinate phase and is returned to extractor 42 by Way of line S. The ranate phase from separator 54 is pased by way of line 61 into Washer 62.

Washer 62 is a countercurrent contacting tower provided with packing to permit eicient contacting of the rainate phase and Water. Water from source 63 is passed through line 64 into an upper point of Washer 62. About 1 volume of water is used per volume of raflinate phase. The temperature of Washing is about that of the wash Water. Oil essentially free of alkanesulfonic acid is withdrawn from washer 62 by way of line 66 and sent to storage not shown. This oil has a high octane number and is suitable for aviation gasoline blending stock. The water and acid are Withdrawn from washer 62 and are passed through line 67 to acid recovery facilities not shown. The acid can be recovered by multiple-effect distillation by methods Well known to this art.

In order to remove the close boiling non-aromatic hydrocarbons from the extract phase an inert wash hydrocarbon is introduced near the bottom of extractor 42. In this illustration the wash hydrocarbon is pentane which is passed from source 71 and line 72 into extractor 42 near the bottom thereof; volume percent based on hydrocarbons in the extract phase is introduced into extractor 42. The pentane in part remains in the extract phase and in part passes out of extractor 42 in the raffinate phase. This latter portion is recovered along with the rainate hydrocarbons and is passed to storage therewith by Way of line 66.

The extract phase is withdrawn from extractor 42 by way of valved line 73 and is passed through heat exchanger 76 and line 77 into a hydrocarbon recovery vessel 73. Vessel 78 is provided with an internal heat exchanger 79. Vessel 78 is operated at a bottoms temperature of about 130 C. and at a pressure of 300 mm. Hg. Substantially all the benzene and toluene present in the extract phase are removed overhead and are passed through line 81, vacuum pump $2, line 83 and heat exchanger 84 into valved line 86. The benzene and toluene are condensed in heat exchanger 34 and are passed as liquids into line 86.

The bottoms from vessel '78 are passed by way of valved line 91 through heat exchanger 92 and line 93 into extractor 94. Heat exchanger 92 reduces the temperature of the bottoms from vessel 78 to a temperature of about C. Extractor 94 is a vessel similar in construction to extractor 42 and provides about five theoretical extraction stages.

Benzene from line 96 is introduced into extractor 94 near the bottom thereof. In this illustration 6 mols of benzene are used per mol of aromatic hydrocarbon present in line 93. A second ranate phase consisting of benzene, C9 and Cio aromatic hydrocarbons is Withdrawn from the top of extractor 94 and is passed by way of line 98 into line 86. The combined stream of benzene and toluene from vessel 78 and the rainate phase from extractor 94 are passed through line 99 into fractionator 101.

Fractionator 101 is provided with internal heat exchanger 102. Fractionator 101 represents a schematic distillation system to separate the contents of line 99 into its major components. Pentane is passed by way of line 104 and other lines not shown to line 72 for reuse in the process. The toluene is passed to storage not shown by Way of line 106. Mixed Ca aromatic hydrocarbons are passed to storage not shown by way of line 107. A bottoms fraction consisting of Cs and C10 aromatic hydrocarbons and trace amounts of alkanesulfonic acids are passed to storage not shown by way of line 168. This fraction can be readily free of acid by a washing operation such as shown in Washer 62 and then separated into close boiling fractions by distillation.

Benzene is Withdrawn from the fractionation system by Way of line 111. A portion of the total benzene is passed by way of valved line 112 and line 113 into line 96 for use in extractor 94. The remainder of the benzene from line 111 is sent to storage not shown by way of .line 116.

The second extract phase from extractor 94 is passed through line 11S, heat exchanger 119 and lline 121 into benzene recovery vessel 122. Vessel 122 is provided with an internal heater 123. Vessel 122 is Ioperated at a temperature of about C. and a pressure of about 300 mm. Hg. The benzene vapors are passed out of vessel 122 through line 126, vacuum pump 127 and line 128 into heat exchanger 129. The vapors are condensed in heat exchanger 129 and are passed by way of lines 131, 113 and 96 into extractor 94.

The bottoms from vessel 122, which consist essenti-ally of a fluid dispersion of solid silver methanesulfonate in a solution of methanesulfonic acid and silver methanesulfonate is withdrawn from vessel 122 and recycled to extractor 42 by way of lines 134 and 54.

It is to be understood that the partial removal of benzene and toluene from the rst extract phase in vessel 78 is not essential. The entire extract phase could be passed into extractor 94. However, in order to reduce the amount of benzene circulating, it is preferred to remove the benzene and toluene before the `displacement operation.

In order to illustrate the results obtainable with this process, several series of runs were made under different conditions. In all these runs the extraction was carried out by simple shaking in a separatory funnel. In each run the feed consisted of 25 ml. of a mixture of n-heptane and a particular aromatic hydrocarbon. The feed consisted approximately of equal volumes of the two components. In each run 20 ml. of the particular alkanesulfonic Iacid was used and the contacting was carried out at room temperature, about 20 C. The procedure consisted of adding the silver salt, the acid and the feed to the contacting vessel, in that order. After the contacting step the contents were settled and the phases separated. The raffinate phase was washed with aqueous caustic solution and the composition determined by refractive index methods. This extract phase was diluted with water and the extract hydrocarbon recovered. The composition of the extract hydrocarbons was determined by refractive index methods.

TEST 1 In this test a series of runs was made to determine the improvement in extraction obtainable by the Iaddition of silver sulfate to a particular alkanesulfonic acid when using various aromatic hydrocarbons in the mixed feed. Each run was carried out as described above. Comparative runs were made at each set of conditions; one run Without silver sulfate, and the other run containing 0.0335 Y The results of these runs are given Table I Feed Ralnate Extract Y Type g. Atom V. Per- Net Moi Run Sulfonic Silver/Mol cent Arom. V. Per Acid Aromatic V. Per- V. Per- V. Per- V. Per- Aromatic Ext./g. Type Aromatic cent cent cent cent cent Extracted Atom Ag Aromatic On Feed Aromatic On Feed Aromatic 91 46 9 91 17 76 33 24 97 49 1. 27 80 39 20 87 36 49 d0 O. 24 64 27 34 92 67 1.13 49 Methane. 94 47 6 70 8 49 d0 0.29 77 33 27 98 54 l. 50 50 d0` 96 49 4 53 4 50 do 0.33 80 38 20 96 38 1.06 50 d0. 97 49 3 57 3 50 d0 0.33 74 35 26 97 50 1.42

Table II Feed n Ranate Extract Type g. Atom V. Per- Net Mol Run Sulfonic Silver/Mol cent Arom. V. Per- Acid Aromatic V. Per- V. Per- V. Per V. Per- Aromatic Ext./g Type 'Aromatic con cent cent cent cent Extracted Atom Ag Aromatic On Feed Aromatic On Feed Aromatic 11 Benzene-., 49 Ethane.-- 80 39 20 87 36 48 d0 0.05 77 36 23 90 43 1. 27 48 ..d0 0. 14 70 70 30 91 56 1. 33 49 do 0.24 66 27 34 92 63 1.13 48 do 0. 29 66 25 34 93 67 1. 06

Table III Feed Ranate Extract Type g. Atom V. Per- Net Mol Run Sulfonic Silver/M01 cent Arom. V. Per- Acid Aromatic V. Per- V. Per- V. Per. V. Per- Aromatic Ext./g. Type Aromatic cent cent cent cent cent Extracted Atom Ag Aromatic On Feed Aromatic On Feed Aromatic 16 Benzene 49 Ethane. l 0. 24 66 27 34 92 63 1.13 49 ..d0 20.24 64 25 36 91 66 1.24 48 Methane.. l 0. 25 76 33 24 97 49 1. 29 48 do I 0.25 74 30 26 97 53 1.45

l Silver sulfate. i Silver ethanesulionate.

TEST 2 TEST 3 In this -test a series of runs were made using the same feed, two diterent acids and using in one instance silver sulfate, and in the other instance silver ethanesulfonate as the silver salts. The purpose of these runs was to determine any diierence in extraction eficiency based on difference in type of silver salt. The data presented in Table III indicate that silver ethanesulfonate is somewhat better than silver sulfate for the extraction of benzene from a benzene-heptane feed.

TEST 4 In this test m-xylene was displaced from an extract phase by contacting the exact phase with benzene. The extract phasewas made up by adding 0.136 mol of rnxylene and 0.062 g. atoms of silver as silver sulfate to ml. of methanesulfonic acid. In each run the standard extract phase was agitated with different `amounts of benzene. The rainate hydrocarbons and extract hydrocarbons were recovered and analyzed for m-xylene and benzene content. The results of this single-stage batchwise contacting show that an added lower molecular weight aromatic hydrocarbon can displace a higher molecular weight aromatic hydrocarbon from an extract phase. The results of this test are shown in Table IV.

Table IV Added Ralnate Extract Bohren@ Run (Mols/Mols Xylene) V. percent V. percent V. percent V. percent m-Xylene Benzene m-Xylene Benzene TEST 5 In this test 25 m1. of a feed mixture consisting of 33 weight percent butylbenzene, 22 weight percent naphthalene and the remainder n-heptane was contacted with 20 ml. of ethanesulfonic acid and 0.021 g. atom of silver as silver sulfate at 20 C. Analysis of the ratiinate hydrocarbons and extract hydrocarbons indicated that naphthalene was preferentially taken into the extract phase. The separation factor a, between butylbenzene and naphthalene, for this run was 17. This test indicates that by the use of the alkanesulfonic acid-silver salt treating agent of this invention it is possible to readily separate dicyclic aromatic hydrocarbons from monocyclic aromatic hydrocarbons.

Thus having described the invention, what is claimed 1. An aromatic hydrocarbon separation process comprising (1) countercurrently contacting under essentially anhydrous conditions at a temperature between 11 about C. and 150 C. a feed consisting essentially of aromatic hydrocarbons and saturated non-aromatic hydrocarbons, said hydrocarbons boiling below about 450 F. with a treating agent consisting of (a) an alkanesulfonic acid having from 1 to 9 carbon atoms and (b) a silver salt selected from the class consisting of silver sulfate and silver alkanesulfonates containing from 1 to 9 carbon atoms wherein said acid is present in an amount between about 50 and 120 volume percent based on said feed and said silver salt is present in an amount of at least about 1 gram atom of silver per mol of aromatic hydrocarbons in said feed, which treating agent contains said silver salt in an amount that exceeds the physical solubility of said silver salt in said alkanesulfonic acid, whereby said treating agent consists of said alkanesulfonic acid, physically dissolved silver salt and solid silver salt particles dispersed in said alkanesulfonic acid, the treating agent appearing to be a liquid, (2) separating a ranate phase from an extract phase comprising treating agent and aromatic hydrocarbons, (3) removing Aessentially all the hydrocarbons from said extract phase by a distillation procedure to recover treating agent consisting of alkanesulfonic acid, physically dissolved silver salt and solid silver salt particles dispersed in said alkanesulfonic acid, the whole appearing to be a liquid, and (4) recycling said recovered treating agent to said contacting zone.

2. The process of claim 1 wherein said temperature is between about 0 C. and 30 C.

3. The process of claim 1 wherein said acid is selected from the class consisting of methanesulfonic, ethanesulfonic, and l-propanesulfonic.

4. The process of claim 1 wherein said feed is a catalytic reformate boiling over the range of about F. to 385 F.

5. The process of claim 3 wherein said salt is silver methanesulfonate.

6. The process of claim 3 wherein said salt is silver ethanesulfonate. K

7. The process of claim 3 wherein said salt is silver sulfate.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Proell et al.: Ind. Eng. Chem., volume 40, pages 1129-32 (1948). 

1. AN AROMATIC HYDROCARBON SEPARATION PROCESS COMPRISING (1) COUNTERCURRENTLY CONTACTING UNDER ESSENTIALLY ANHYDROUS CONDITIONS AT A TEMPERATURE BETWEEN ABOUT 0* C. AND 150* C. A FEED CONSISTING ESSENTIALLY OF AROMATIC HYDROCARBONS AND SATURATED NON-AROMATIC HYDROCARBONS, SAID HYDROCARBONS BOILING BELOW ABOUT 450* F. WITH A TREATING AGENT CONSISTING OF (A) AN ALKANESULFONIC ACID HAVING FROM 1 TO 9 CARBON ATOMS AND (B) A SILVER SALT SELECTED FROM THE CLASS CONSISTING OF SILVER SULFATE AND SILVER ALKANESULFONATES CONTAINING FROM 1 TO 9 CARBON ATOMS WHEREIN SAID ACID IS PRESENT IN AN AMOUNT BETWEEN ABOUT 50 AND 120 VOLUME PERCENT BASED ON SAID FEED AND SAID SILVER SALT IS PRESENT IN AN AMOUNT OF AT LEAST ABOUT 1 GRAM ATOM OF SILVER PER MOL OF AROMATIC HYDROCARBONS IN SAID FEED, WHICH TREATING AGENT CONTAINS SAID SILVER SALT IN AN AMOUNT THAT EXCEEDS THE PHYSICAL SOLUBILITY OF SAID SILVER SALT IN SAID ALKANESULFONIC ACID, WHEREBY SAID TREATING AGENT CONSISTS OF SAID ALKANESULFONIC ACID, PHYSICALLY DISSOLVED SILVER SALT AND SOLID SILVER SALT PARTICLES DISPERSED IN SAID ALKANESULFONIC ACID, THE TREATING AGENT APPEARING TO BE A LIQUID, (2) SEPARATING A RAFFINATE PHASE FROM AN EXTACT PHASE COMPRISING TREATING AGENT AND AROMATIC HYDROCARBONS (3) REMOVING ESSENTIALLY ALL THE HYDROCARBONS FROM SAID EXTRACT PHASE BY A DISTILLATION PROCEDURE TO RECOVER TREATING AGENT CONSISTING OF ALKANESULFONIC ACID, PHYSICALLY DISSOLVED SILVER SALT AND SOLID SILVER SALT PARTICLES DISPERSED IN SAID ALKANESULFONIC ACID, THE WHOLE APPEARING TO BE A LIQUID, AND (4) RECYCLING SAID RECOVERED TREATING AGENT TO SAID CONTACTING ZONE. 